Well wall reinforced oil-based drilling fluid system and preparation method thereof

Abstract

The invention belongs to the technical field of drilling fluid, and relates to a well wall reinforced oil-based drilling fluid system and a preparation method thereof. The system comprises the following components in parts by mass: 100 parts of a solvent, 3-4 parts of organic soil, 5-7 parts of an emulsifier, 2-4 parts of an oil-based filtrate reducer, 20-25 parts of saline water, 1.5-3 parts of a lubricant, 1-3 parts of a micro-nano plugging agent, 2-3 parts of a viscosity reducer and 60-80 parts of barite, the nano blocking agent comprises nano silicon dioxide particles with oleophylic groups distributed on the surfaces. On the basis of containing a micro-nano blocking agent, other well wall reinforced oil-based drilling fluid treating agent materials are screened, optimized and modified to obtain a well wall reinforced oil-based drilling fluid system, the micro-nano blocking agent is good in compatibility with an on-site drilling fluid system, and after the micro-nano blocking agent is added, the on-site drilling fluid is stable in performance and good in rheological property; the nano-micron plugging agent has a remarkable effect in the aspect of well wall reinforcement.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of drilling fluids, and relates to a well wall reinforced oil-based drilling fluid system and a preparation method. BACKGROUND

[0002] There are many layering, microfractures and pores in shale gas formations, and well wall instability is prone to occur during drilling. Well wall instability refers to the fact that, during wellbore drilling, the matching degree of the mechanical properties of the formation rock and the consolidation quality of the well wall is not enough, resulting in instability phenomena such as collapse and rupture of the well wall. This phenomenon can affect the efficiency and safety of drilling work, and may even cause accidents. In the study of well wall stability, factors that affect well wall stability usually include the effects of hydration and pressure transmission.

[0003] Oil-based drilling fluids have excellent inhibitory, lubricating and high-temperature stability, and have achieved remarkable results in drilling complex prevention and control and horizontal section extension, but the oil phase often invades during drilling, causing well wall instability and thus triggering a series of downhole complications. Therefore, a plugging agent for drilling fluids is used to increase the supporting capacity of the drilling fluid for the well wall and prevent the collapse of the well wall. The application of nanometer plugging agents can improve the performance of the drilling fluid and improve the stability of the well wall, and can fill the pores and microfractures of the well wall, thereby reducing problems such as well wall collapse and loss during drilling.

[0004] At present, drilling fluid plugging agents are mainly based on polymer nanocomposites. A company has developed a deformable nanoscale plugging polymer MAX-SHIELD, the main component of which is carboxyl styrene butadiene latex or sulfonated styrene butadiene latex with an average particle size of less than 0.2 nm. When the addition amount is 3%, a dense film structure can be formed on the surface of the well wall, achieving good plugging effect and well wall stability. However, its price is relatively high, and its compatibility with other treatment agents and inorganic salts is not strong, which leads to its inability to be widely used in oilfields.

[0005] Therefore, resin-based plugging agents are still the mainstream products in the market, but they are high in cost and have no selectivity, and are usually limited to within 30 cm in the radial direction around the static bottom during use, and must be detected and isolated before use. The resin is sensitive to water, surfactants, alkali and acid before curing, and must be paid attention to during use.

[0006] Therefore, there is an urgent need to develop a new well wall reinforced oil-based drilling fluid system that is low in price and good in effect. SUMMARY

[0007] The purpose of the present application is to provide a well wall reinforced oil-based drilling fluid system and a preparation method, which can effectively solve the problem that oil-based drilling fluids cannot be compatible in cost and plugging effect.

[0008] The present application is achieved by the following technical solutions: A wellbore reinforcement oil-based drilling fluid system, comprising the following components by mass parts: 100 parts solvent, 3-4 parts organic clay, 5-7 parts emulsifier, 2-4 parts oil-based filtration reducer, 20-25 parts brine, 1.5-3 parts lubricant, 1-3 parts micro / nano sealing agent, 2-3 parts viscosity reducer, and 60-80 parts barite; The micro / nano plugging agent comprises nano-silica particles with lipophilic groups distributed on their surface.

[0009] Furthermore, the solvent is selected from one or more of white oil and water; The salt water is calcium chloride salt water.

[0010] Furthermore, the oil-based filtration reducer is a resin-modified product with sulfonic acid groups as the main component.

[0011] Furthermore, the lubricant is a liquid lubricant.

[0012] Furthermore, the viscosity reducer is an oil-soluble viscosity reducer.

[0013] Furthermore, the emulsifier includes a primary emulsifier and a secondary emulsifier; The primary emulsifier is an anionic surfactant, and the secondary emulsifier is a nonionic surfactant.

[0014] Furthermore, the lipophilic group is polystyrene; the lipophilic group is attached to the nano-silica particles by a silane coupling agent.

[0015] Furthermore, the silane coupling agent is selected from one or more of KH-550, KH-570, KBM-903, A-172 and γ-MPS.

[0016] This invention also discloses a method for preparing the wellbore-enhancing oil-based drilling fluid system, comprising the following steps: S1. Add emulsifier and lubricant to solvent and stir continuously for 4-6 hours to form oil-based slurry; S2. Then, gradually add brine during the stirring process to form a simple water-in-oil drilling fluid system, and continue stirring for 6 to 12 hours. S3. Then, under stirring conditions, add organic soil, oil-based filtration reducer, micro-nano plugging agent, viscosity reducer and barite, and continue stirring and curing to form a stable colloidal suspension system, thus obtaining the wellbore strengthening oil-based drilling fluid system.

[0017] Furthermore, the preparation method of the micro / nano plugging agent is as follows: (1) Add nano-silica to water, then add silane coupling agent, and disperse by ultrasonication to obtain mixture A; Mixture A was heated in a water bath while stirring, and then centrifuged to obtain the product. The product was dried to obtain APTES-SiO2; (2) APTES-SiO2 was ultrasonically dispersed in water, and styrene, buffer, sodium dodecyl sulfate and nonylphenol polyoxyethylene ether were added. The mixture was stirred in a water bath and nitrogen was introduced to remove air, thus obtaining a pre-emulsion. (3) Add the initiator to the pre-emulsion and stir in a water bath to obtain mixture B; (4) Centrifuge, wash and dry the mixture B to obtain PS-SiO2, which is a micro-nano sealing agent.

[0018] Compared with the prior art, the present invention has the following beneficial technical effects: This invention discloses a wellbore-enhancing oil-based drilling fluid system, comprising micro / nano plugging agent, organic clay, emulsifier, oil-based filtration reducer, brine, viscosity reducer, and barite. The organic clay is used to improve wellbore cleaning ability, form mud cake, and improve wellbore stability. The emulsifier is used to emulsify and disperse the oil-based drilling fluid. The oil-based filtration reducer is used to reduce filtration loss. The brine is used to improve the solubility and stability of the drilling fluid system, reduce the adsorption of the oil-based filtration reducer, and make it more stable. The lubricant is used to reduce friction in the drilling fluid system and improve lubricity. The micro / nano plugging agent is used to improve plugging performance and enhance wellbore stability. The viscosity reducer is used to reduce the viscosity of the drilling fluid system. The addition of barite is mainly to increase the density of the drilling fluid. During drilling, high-pressure fluids may exist in the formation; by increasing the density of the drilling fluid, the formation pressure can be effectively balanced, preventing dangerous situations such as blowouts.

[0019] Based on micro-nano plugging agents, and through screening other wellbore strengthening oil-based drilling fluid treatment agents, a wellbore strengthening oil-based drilling fluid system was obtained after optimization and modification. The micro-nano plugging agents have good compatibility with the field drilling fluid system. After adding micro-nano plugging agents, the field drilling fluid performance is stable and has good rheological properties. The nano-micro plugging agents have significant effects on wellbore strengthening.

[0020] Furthermore, the nano-micro plugging agent prepared by this invention has low cost and good plugging effect.

[0021] Firstly, the low cost is mainly due to the following reasons: nano-silica is a common industrial raw material with a relatively low price; styrene is also a widely used chemical raw material with ample market supply and a relatively stable price. The amount of additives used in the preparation process, such as silane coupling agents, buffers, sodium dodecyl sulfate, and nonylphenol polyoxyethylene ether, is relatively small, resulting in lower costs.

[0022] The preparation method of this plugging agent adopts conventional processes such as water bath heating, stirring, and ultrasonic dispersion, requiring low equipment and being simple to operate. It eliminates the need for complex production equipment and energy-intensive processes, reducing production costs. Furthermore, the preparation process does not require expensive catalysts or special reaction conditions, further reducing costs.

[0023] This preparation method exhibits good repeatability and stability, making it suitable for large-scale production. Production costs can be further reduced by optimizing the production process and improving efficiency.

[0024] Secondly, the good sealing effect is mainly due to the surface modification of nano-silica using silane coupling agents, which gives the surface active groups, enabling it to better bond with styrene. The PS-SiO2 sealing agent formed by the polymerization of modified nano-silica and styrene has higher bonding strength and stability, and can better seal pores and fractures in the formation.

[0025] Surface modification also improves the dispersibility of nano-silica in water, allowing it to be distributed more evenly in the plugging agent and improving the plugging effect.

[0026] The polymerization of styrene on the surface of nano-silica to form a polymer coating layer not only improves the stability of the plugging agent but also increases its compatibility with the formation. The polymer coating layer can prevent the aggregation and precipitation of nano-silica particles, keeping them well dispersed in fluids.

[0027] When in contact with the formation, the polymer coating can interact with the materials in the formation, forming a stronger bond and improving the sealing effect.

[0028] Nano-silica and styrene polymers work synergistically in the sealing process. The small size of nano-silica allows it to penetrate deep into micropores and cracks, forming the first line of defense; while the styrene polymer forms a robust coating layer around the nano-silica, further enhancing the sealing effect.

[0029] The synergistic effect of the two enables the plugging agent to adapt to different types of formations and complex formation environments, achieving efficient plugging. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the present invention clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of the present invention, and not all of them.

[0031] The detailed description of the embodiments of the present invention provided below is not intended to limit the scope of the claimed invention, but merely to illustrate one selected embodiment of the invention.

[0032] This invention discloses a wellbore strengthening oil-based drilling fluid system, comprising the following components by mass: The mixture contains 100 parts solvent, 3 parts organic clay, 5-7 parts emulsifier, 2-4 parts oil-based filtration reducer, 24-25 parts brine, 1.5-3 parts lubricant, 1 part micro / nano plugging agent, 2 parts viscosity reducer, and 80 parts barite; the micro / nano plugging agent comprises nano-silica particles with lipophilic groups distributed on their surface.

[0033] The preparation method of the micro / nano plugging agent is as follows: (1) Add nano-silica to water, then add silane coupling agent, and disperse by ultrasonication to obtain a mixture; The mixture was heated in a water bath while being stirred, and then centrifuged to obtain the product. The product was dried to obtain APTES-SiO2; (2) The APTES-SiO2 obtained in step (1) is ultrasonically dispersed in water, and styrene, buffer, sodium dodecyl sulfate, and nonylphenol polyoxyethylene ether are added. The mixture is stirred in a water bath and nitrogen is introduced to remove air, thus obtaining a pre-emulsion. (3) Add potassium persulfate to the pre-emulsion and stir in a water bath; (4) Add potassium persulfate to the mixture obtained in step (3), react, and obtain a mixture; (5) The mixture obtained in step (4) is centrifuged and washed to obtain the product; (6) Dry the product obtained in step (5) to obtain PS-SiO2, which is a micro-nano sealing agent.

[0034] The emulsifier includes a primary emulsifier and a secondary emulsifier; the primary emulsifier is an anionic surfactant, and the secondary emulsifier is a nonionic surfactant.

[0035] Specifically, the primary emulsifier is alkylphenol polyoxyethylene ether (OP-10), and the secondary emulsifier is sodium dodecyl sulfate (SDS).

[0036] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0037] Example 1 Based on mass parts, this embodiment discloses a wellbore strengthening oil-based drilling fluid system, comprising: 100 parts water, 3 parts organic clay, 6 parts emulsifier (OP-10+SDS), 2 parts oil-based filtration reducer (sulfonated resin BZ-OFL), 25 parts calcium chloride brine, 1.5 parts liquid lubricant (BZ-OSE), 1 part micro-nano plugging agent, 2 parts viscosity reducer (oil-soluble viscosity reducer (YL-2)), and 60 parts barite.

[0038] The method for preparing the wellbore-enhancing oil-based drilling fluid system includes the following steps: S1. Add emulsifier and lubricant to solvent and stir continuously for 4 hours to form oil-based slurry; S2. Then, gradually add brine during the stirring process to form a simple water-in-oil drilling fluid system, and continue stirring for 6 hours. S3. Then, under stirring conditions, add organic soil, oil-based filtration reducer, micro-nano plugging agent, viscosity reducer and barite, and continue stirring and curing to form a stable colloidal suspension system, thus obtaining the wellbore strengthening oil-based drilling fluid system.

[0039] The preparation method of the micro / nano plugging agent in this embodiment is as follows: (1) Add 30 g of silica micro-nanospheres to 300 mL of water, and then add 0.92 g of silane coupling agent KH-550 (APTES) to obtain mixture 1.

[0040] Mixture 1 was ultrasonically dispersed for 30 min, then stirred at 400 rpm for 30 min, and then stirred at 400 rpm for 30 min in a 60 ℃ water bath. It was then centrifuged to obtain solid product 1, which was dried to obtain silane coupling agent modified silica micro / nanospheres (APTES-SiO2).

[0041] (2) Add 20g APTES-SiO2 to 300 mL of water and sonicate for 30 min. Then add 3g styrene, 2.0g NaHCO3, 2.0g sodium dodecyl sulfate (SDS) and 1.0g nonylphenol polyoxyethylene ether (OP-10) surfactant to obtain mixture 2.

[0042] Mixture 2 was stirred at 350 rpm for 4 h in a 65 ℃ water bath, and then nitrogen was purged to remove air, resulting in a pre-emulsion.

[0043] (3) Add 2 g of potassium persulfate initiator to the pre-emulsion and stir at 350 rpm for 30 min in a water bath at 65 ℃. Add another 2 g of potassium persulfate initiator and react at 65 ℃ for 4 h to obtain mixture 3.

[0044] (4) Then the mixture 3 is centrifuged to obtain solid product 2. Solid product 2 is washed with ethanol and then dried to obtain polystyrene silica micro-nanospheres (PS-SiO2) with polystyrene distributed on the surface.

[0045] Thermogravimetric analysis of the PS-SiO2 prepared in this embodiment showed obvious weight loss peaks in the range of 356.3-466.6 °C, indicating that PS-SiO2 has excellent thermal stability.

[0046] The drilling fluid in Example 1 was evaluated for its overall performance according to the above-described performance testing method. The results are shown in Table 1.

[0047] Table 1 Example Drilling Fluid Performance of Example 1

[0048] Notes: Aging conditions: 120℃×48h; HTHP: 120℃, 3.5MPa; Density: 1.3g / cm³ 3 Aging is used to simulate the high-temperature environment of the formation. The drilling fluid is placed in an aging tank and then heated in an oven. The results before and after aging indicate that the drilling fluid has good temperature resistance.

[0049] The wellbore-enhancing oil-based drilling fluid system prepared in this embodiment was tested at concentrations of 1.3, 1.6, and 1.9 g·cm³. -3 It exhibits stable performance under various density conditions, with moderate viscosity, shear stress, and filtration loss. The API filtration loss is no higher than 2 mL, and the HTHP filtration loss is 3.2 mL. The wellbore-enhancing oil-based drilling fluid has a demulsification voltage of 862V and maintains stable performance after hot rolling at 150℃ for 48 hours. The wellbore-enhancing oil-based drilling fluid system demonstrates excellent plugging performance.

[0050] Example 2 Based on mass parts, this embodiment discloses a wellbore strengthening oil-based drilling fluid system, comprising 100 parts white oil, 3 parts organic clay, 5 parts emulsifier (OP-10+SDS), 4 parts oil-based filtration reducer (sulfonated resin BZ-OFL), 24 parts calcium chloride brine, 1.5 parts liquid lubricant (BZ-OSE), 1.5 parts micro-nano plugging agent, 2 parts viscosity reducer (oil-soluble viscosity reducer (YL-2)), and 70 parts barite.

[0051] The method for preparing the wellbore-enhancing oil-based drilling fluid system includes the following steps: S1. Add emulsifier and lubricant to solvent and stir continuously for 5 hours to form oil-based slurry; S2. Then, gradually add brine during the stirring process to form a simple water-in-oil drilling fluid system, and continue stirring for 6 hours. S3. Then, under stirring conditions, add organic soil, oil-based filtration reducer, micro-nano plugging agent, viscosity reducer and barite, and continue stirring and curing to form a stable colloidal suspension system, thus obtaining the wellbore strengthening oil-based drilling fluid system.

[0052] The method for preparing the wellbore-enhancing oil-based drilling fluid system includes the following steps: S1. Add emulsifier and lubricant to solvent and stir continuously for 4 hours to form oil-based slurry; S2. Then, gradually add brine during the stirring process to form a simple water-in-oil drilling fluid system, and continue stirring for 6 hours. S3. Then, under stirring conditions, add organic soil, oil-based filtration reducer, micro-nano plugging agent, viscosity reducer and barite, and continue stirring and curing to form a stable colloidal suspension system, thus obtaining the wellbore strengthening oil-based drilling fluid system.

[0053] The preparation method of the micro / nano plugging agent in this embodiment is as follows: (1) Add 30 g of silica micro-nanospheres to 300 mL of water, and then add 0.92 g of silane coupling agent KH-570 (APTES) to obtain mixture 1.

[0054] Mixture 1 was ultrasonically dispersed for 30 min, then stirred at 400 rpm for 30 min, and then stirred at 400 rpm for 30 min in a 60 ℃ water bath. It was then centrifuged to obtain solid product 1, which was dried to obtain silane coupling agent modified silica micro / nanospheres (APTES-SiO2).

[0055] (2) Add 20g APTES-SiO2 to 300 mL of water and sonicate for 30 min. Then add 3g styrene, 2.0g NaHCO3, 2.0g sodium dodecyl sulfate (SDS) and 1.0g nonylphenol polyoxyethylene ether (OP-10) surfactant to obtain mixture 2.

[0056] Mixture 2 was stirred at 350 rpm for 4 h in a 70 ℃ water bath, and then nitrogen was purged to remove air, resulting in a pre-emulsion.

[0057] (3) Add 2 g of potassium persulfate initiator to the pre-emulsion and stir at 350 rpm for 30 min in a water bath at 65 ℃. Add another 2 g of potassium persulfate initiator and react at 65 ℃ for 4 h to obtain mixture 3.

[0058] (4) Then the mixture 3 is centrifuged to obtain solid product 2. Solid product 2 is washed with ethanol and then dried to obtain polystyrene silica micro-nanospheres (PS-SiO2) with polystyrene distributed on the surface.

[0059] The drilling fluid in Example 2 was evaluated for its overall performance according to the above-described performance testing method. The results are shown in Table 2.

[0060] Table 2 Example Drilling Fluid Performance of Example 2

[0061] Notes: Aging conditions: 120℃×48h; HTHP: 120℃, 3.5MPa; Density: 1.6g / cm³ 3 The wellbore-enhancing oil-based drilling fluid system prepared in this embodiment was tested at concentrations of 1.3, 1.6, and 1.9 g·cm³. -3 It exhibits stable performance under various density conditions, with moderate viscosity, shear stress, and filtration loss. The API filtration loss is no higher than 2 mL, and the HTHP filtration loss is 3.8 mL. The wellbore-enhancing oil-based drilling fluid has a demulsification voltage of 781V, and its performance remains stable after hot rolling at 150℃ for 48 hours. The wellbore-enhancing oil-based drilling fluid system demonstrates excellent plugging performance.

[0062] Example 3 This embodiment discloses a wellbore strengthening oil-based drilling fluid system by mass, comprising 100 parts water, 3 parts organic clay, 7 parts emulsifier (OP-10+SDS), 2 parts oil-based filtration reducer (sulfonated resin BZ-OFL), 20 parts calcium chloride brine, 2 parts liquid lubricant (BZ-OSE), 2 parts micro-nano plugging agent, 3 parts viscosity reducer (oil-soluble viscosity reducer (YL-2)), and 75 parts barite.

[0063] The method for preparing the wellbore-enhancing oil-based drilling fluid system includes the following steps: S1. Add emulsifier and lubricant to solvent and stir continuously for 4 hours to form oil-based slurry; S2. Then, gradually add brine during the stirring process to form a simple water-in-oil drilling fluid system, and continue stirring for 6 hours. S3. Then, under stirring conditions, add organic soil, oil-based filtration reducer, micro-nano plugging agent, viscosity reducer and barite, and continue stirring and curing to form a stable colloidal suspension system, thus obtaining the wellbore strengthening oil-based drilling fluid system.

[0064] The preparation method of the micro / nano plugging agent in this embodiment is as follows: (1) Add 30 g of silica micro-nanospheres to 300 mL of water, and then add 0.92 g of silane coupling agent KBM-903 (APTES) to obtain mixture 1.

[0065] Mixture 1 was ultrasonically dispersed for 30 min, then stirred at 400 rpm for 30 min, and then stirred at 400 rpm for 30 min in a 60 ℃ water bath. It was then centrifuged to obtain solid product 1, which was dried to obtain silane coupling agent modified silica micro / nanospheres (APTES-SiO2).

[0066] (2) Add 20g APTES-SiO2 to 300 mL of water and sonicate for 30 min. Then add 3g styrene, 2.0g NaHCO3, 2.0g sodium dodecyl sulfate (SDS) and 1.0g nonylphenol polyoxyethylene ether (OP-10) surfactant to obtain mixture 2.

[0067] Mixture 2 was stirred at 350 rpm for 4 h in a 60 ℃ water bath, and then nitrogen was purged to remove air, resulting in a pre-emulsion.

[0068] (3) Add 2 g of potassium persulfate initiator to the pre-emulsion and stir at 350 rpm for 30 min in a water bath at 65 ℃. Add another 2 g of potassium persulfate initiator and react at 65 ℃ for 4 h to obtain mixture 3.

[0069] (4) Then the mixture 3 is centrifuged to obtain solid product 2. Solid product 2 is washed with ethanol and then dried to obtain polystyrene silica micro-nanospheres (PS-SiO2) with polystyrene distributed on the surface.

[0070] The drilling fluid in Example 3 was evaluated for its overall performance according to the above-described performance testing method. The results are shown in Table 3.

[0071] Table 3 Example Drilling Fluid Performance of Example 3

[0072] Notes: Aging conditions: 120℃×48h; HTHP: 120℃, 3.5MPa; Density: 1.9g / cm³ 3 The wellbore-enhancing oil-based drilling fluid system prepared in this embodiment was tested at concentrations of 1.3, 1.6, and 1.9 g·cm³. -3 It exhibits stable performance under various density conditions, with moderate viscosity, shear stress, and filtration loss. The API filtration loss is no higher than 2 mL, and the HTHP filtration loss is 5.6 mL. The wellbore-enhancing oil-based drilling fluid has a demulsification voltage of 649V and maintains stable performance after hot rolling at 150℃ for 48 hours. The wellbore-enhancing oil-based drilling fluid system demonstrates excellent plugging performance.

[0073] Example 4 Based on mass parts, this embodiment discloses a wellbore strengthening oil-based drilling fluid system, comprising: 100 parts water, 4 parts organic clay, 6.5 parts emulsifier (OP-10+SDS), 2 parts oil-based filtration reducer (sulfonated resin BZ-OFL), 25 parts brine, 3 parts liquid lubricant (BZ-OSE), 3 parts micro-nano plugging agent, 2 parts viscosity reducer (oil-soluble viscosity reducer (YL-2)), and 80 parts barite.

[0074] The method for preparing the wellbore-enhancing oil-based drilling fluid system includes the following steps: S1. Add emulsifier and lubricant to solvent and stir continuously for 6 hours to form oil-based slurry; S2. Then, gradually add brine during the stirring process to form a simple water-in-oil drilling fluid system, and continue stirring for 12 hours. S3. Then, under stirring conditions, add organic soil, oil-based filtration reducer, micro-nano plugging agent, viscosity reducer and barite, and continue stirring and curing to form a stable colloidal suspension system, thus obtaining the wellbore strengthening oil-based drilling fluid system.

[0075] The preparation method of the micro / nano plugging agent in this embodiment is as follows: (1) Add 30 g of silica micro-nanospheres to 300 mL of water, and then add 0.92 g of silane coupling agent A-172 and γ-MPS (APTES) to obtain mixture 1.

[0076] Mixture 1 was ultrasonically dispersed for 30 min, then stirred at 400 rpm for 30 min, and then stirred at 400 rpm for 30 min in a 60 ℃ water bath. It was then centrifuged to obtain solid product 1, which was dried to obtain silane coupling agent modified silica micro / nanospheres (APTES-SiO2).

[0077] (2) Add 20g APTES-SiO2 to 300 mL of water and sonicate for 30 min. Then add 3g styrene, 2.0g NaHCO3, 2.0g sodium dodecyl sulfate (SDS) and 1.0g nonylphenol polyoxyethylene ether (OP-10) surfactant to obtain mixture 2.

[0078] Mixture 2 was stirred at 350 rpm for 4 h in a 65 ℃ water bath, and then nitrogen was purged to remove air, resulting in a pre-emulsion.

[0079] (3) Add 2 g of potassium persulfate initiator to the pre-emulsion and stir at 350 rpm for 30 min in a 70 ℃ water bath. Add another 2 g of potassium persulfate initiator and react at 70 ℃ for 4 h to obtain mixture 3.

[0080] (4) Then the mixture 3 is centrifuged to obtain solid product 2. Solid product 2 is washed with ethanol and then dried to obtain polystyrene silica micro-nanospheres (PS-SiO2) with polystyrene distributed on the surface.

[0081] The drilling fluid in Example 4 was evaluated for its overall performance according to the above-described performance testing method. The results are shown in Table 4.

[0082] Table 4. Drilling fluid performance in Example 4

[0083] Notes: Aging conditions: 120℃×48h; HTHP: 120℃, 3.5MPa; Density: 1.9g / cm³ 3 The wellbore-enhancing oil-based drilling fluid system prepared in this embodiment has a viscosity of 1.3 g·cm⁻¹. -3 1.6 g·cm -3 1.9 g·cm -3 It exhibits stable performance under various density conditions, with moderate viscosity, shear stress, and filtration loss. The API filtration loss is no higher than 2 mL, and the HTHP filtration loss is 4.5 mL. The wellbore-enhancing oil-based drilling fluid has a demulsification voltage of 659V and maintains stable performance after hot rolling at 150℃ for 48 hours. The wellbore-enhancing oil-based drilling fluid system demonstrates excellent plugging performance.

[0084] The preparation methods of the micro / nano plugging agents in Examples 2-4 are the same as those in Example 1.

[0085] Comparative Example D1: This comparative example provides a wellbore strengthening oil-based drilling fluid system without micro / nano plugging agents. By mass, it includes 100 parts water, 3 parts organic clay, 6 parts emulsifier (OP-10+SDS), 2 parts oil-based filtration reducer (sulfonated resin BZ-OFL), 25 parts calcium chloride brine, 1.5 parts liquid lubricant (BZ-OSE), 1 part ordinary plugging agent, 2 parts viscosity reducer (oil-soluble viscosity reducer (YL-2)), and 60 parts barite.

[0086] Unlike Example 1, the micro / nano plugging agent in Example 1 was replaced with a conventional plugging agent.

[0087] The drilling fluid in Comparative Example 1 was evaluated for its overall performance using the performance testing methods described above. The results are shown in Table 5.

[0088] Table 5. Drilling fluid performance of Comparative Example 1

[0089] Notes: Aging conditions: 120℃×48h; HTHP: 120℃, 3.5MPa; Density: 1.9g / cm³ 3 Comparative Example D2: This comparative example provides a wellbore strengthening oil-based drilling fluid system without micro / nano plugging agents. By mass, it includes 100 parts white oil, 3 parts organic clay, 5 parts emulsifier (OP-10+SDS), 4 parts oil-based filtration reducer (sulfonated resin BZ-OFL), 24 parts calcium chloride brine, 1.5 parts liquid lubricant (BZ-OSE), 1.5 parts ordinary plugging agent, 2 parts viscosity reducer (oil-soluble viscosity reducer (YL-2)), and 70 parts barite.

[0090] Unlike Example 2, the micro / nano plugging agent in Example 2 was replaced with a conventional plugging agent.

[0091] The drilling fluid in Comparative Example 2 was evaluated for its overall performance using the performance testing methods described above. The results are shown in Table 6.

[0092] Table 6. Drilling fluid performance of Comparative Example 2

[0093] Notes: Aging conditions: 120℃×48h; HTHP: 120℃, 3.5MPa; Density: 1.9g / cm³ 3 Comparative Example D3: This comparative example provides a wellbore strengthening oil-based drilling fluid system without micro / nano plugging agents. By mass, it contains 100 parts water, 3 parts organic clay, 7 parts emulsifier (OP-10+SDS), 2 parts oil-based filtration reducer (sulfonated resin BZ-OFL), 20 parts calcium chloride brine, 2 parts liquid lubricant (BZ-OSE), 2 parts ordinary plugging agent, 3 parts viscosity reducer (oil-soluble viscosity reducer (YL-2)), and 75 parts barite.

[0094] Unlike Example 3, the micro / nano plugging agent in Example 3 was replaced with a conventional plugging agent.

[0095] The drilling fluid in Comparative Example 3 was evaluated for its overall performance using the performance testing methods described above. The results are shown in Table 7.

[0096] Table 7. Drilling fluid performance of Comparative Example 3

[0097] Notes: Aging conditions: 120℃×48h; HTHP: 120℃, 3.5MPa; Density: 1.9g / cm³ 3 Comparative Example D4: This comparative example provides a wellbore strengthening oil-based drilling fluid system without micro / nano plugging agents. By mass, it includes 100 parts water, 4 parts organic clay, 6.5 parts emulsifier (OP-10+SDS), 2 parts oil-based filtration reducer (sulfonated resin BZ-OFL), 25 parts brine, 3 parts liquid lubricant (BZ-OSE), 3 parts ordinary plugging agent, 2 parts viscosity reducer (oil-soluble viscosity reducer (YL-2)), and 80 parts barite.

[0098] Unlike Example 4, the micro / nano plugging agent in Example 4 was replaced with a conventional plugging agent.

[0099] The drilling fluid in Comparative Example 4 was evaluated for its overall performance using the performance testing methods described above. The results are shown in Table 8.

[0100] Table 8. Drilling fluid performance of Comparative Example 4

[0101] Notes: Aging conditions: 120℃×48h; HTHP: 120℃, 3.5MPa; Density: 1.9g / cm³ 3 The above comparison shows that the drilling fluid system with added micro-nano plugging agents has better rheological properties and lower API filtration loss and high-temperature and high-pressure filtration loss.

[0102] The performance testing methods involved in the above examples are as follows: 1. Evaluation of filtration performance of oil-based drilling fluid systems: The filtration volume of the wellbore-enhancing oil-based drilling fluid system prepared according to this invention was determined using a medium-pressure filtration loss meter. The specific process is as follows: Pour 150 mL of the prepared drilling fluid into the medium-pressure filtration analyzer, place the gasket and special filter paper, close the lid and tighten the seal. Record the volume of filtrate within 30 minutes at an output pressure of 0.69 MPa. This volume is the medium-pressure API filtration loss of the drilling fluid, in mL.

[0103] 2. Evaluation of HTHP filtration performance of oil-based drilling fluids: Pour 150 mL of the prepared drilling fluid into a mud cup, install the special filter paper for testing HTHP filtration loss, seal it, and place it in a high-temperature, high-pressure filtration loss meter (MJ-71, Modern Petroleum Technology Development Co., Ltd.). After heating to 150℃, connect the pressure valve stem and the back pressure valve stem, maintaining the pressure at 4.2 MPa and the back pressure at 0.7 MPa. Record the volume of filtrate after 30 minutes of filtration loss. Multiply the filtrate volume by 2 to obtain the HTHP filtration loss.

[0104] 3. Evaluation of the rheological properties of water-based drilling fluids: The reference data for drilling fluid rheological properties include apparent viscosity, plastic viscosity, dynamic shear force, and static shear force. After stirring the oil-based drilling fluid at a high-frequency speed of 12,000 rpm for 20 min, the values ​​for the water-based drilling fluid were measured using a six-speed rotational viscometer at drilling speeds of 600 rpm and 300 rpm, according to standard GB / T 16782-1997. The values ​​were also measured at a drilling speed of 3 rpm after stirring at 600 rpm for 1 min and then allowing the fluid to stand for 10 s and 10 min, respectively. The apparent viscosity (AV), plastic viscosity (PV), and dynamic shear force (YP) of the water-based drilling fluid were calculated using the following formulas.

[0105] (1) Apparent viscosity AV (unit mPa·s) = 0.511 * Φ600 (2) Plastic viscosity PV (unit mPa·s) = Φ600 - Φ300 (3) Dynamic shear force (unit Pa) YP=0.511*(Φ300-PV) (4), initial cut (τ 初 = 0.511 * Φ3 (after standing for 10 seconds) Final cut (τ) 终 = 0.511 * Φ3 (let stand for 10 minutes) Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A wellbore strengthening oil-based drilling fluid system, characterized in that, Based on parts by mass, it includes the following components: 100 parts solvent, 3-4 parts organic clay, 5-7 parts emulsifier, 2-4 parts oil-based filtration reducer, 20-25 parts brine, 1.5-3 parts lubricant, 1-3 parts micro / nano sealing agent, 2-3 parts viscosity reducer, and 60-80 parts barite; The micro / nano plugging agent comprises nano-silica particles with lipophilic groups distributed on their surface.

2. The wellbore reinforcement oil-based drilling fluid system according to claim 1, characterized in that, The solvent is selected from one or more of white oil and water; The salt water is calcium chloride salt water.

3. The wellbore reinforcement oil-based drilling fluid system according to claim 1, characterized in that, The oil-based filtration reducer is a resin-modified product with sulfonic acid groups as the main component.

4. The wellbore reinforcement oil-based drilling fluid system according to claim 1, characterized in that, The lubricant is a liquid lubricant.

5. The wellbore reinforcement oil-based drilling fluid system according to claim 1, characterized in that, The viscosity reducer is an oil-soluble viscosity reducer.

6. The wellbore reinforcement oil-based drilling fluid system according to claim 1, characterized in that, The emulsifier includes a primary emulsifier and a secondary emulsifier; The primary emulsifier is an anionic surfactant, and the secondary emulsifier is a nonionic surfactant.

7. A wellbore reinforcement oil-based drilling fluid system according to any one of claims 1-6, characterized in that, The lipophilic group is polystyrene; the lipophilic group is attached to the nano-silica particles by a silane coupling agent.

8. The wellbore reinforcement oil-based drilling fluid system according to claim 7, characterized in that, The silane coupling agent is selected from one or more of KH-550, KH-570, KBM-903, A-172 and γ-MPS.

9. A method for preparing the wellbore reinforcement oil-based drilling fluid system according to any one of claims 1-8, characterized in that, Includes the following steps: S1. Add emulsifier and lubricant to solvent and stir continuously for 4-6 hours to form oil-based slurry; S2. Then, gradually add brine during the stirring process to form a simple water-in-oil drilling fluid system, and continue stirring for 6 to 12 hours. S3. Then, under stirring conditions, add organic soil, oil-based filtration reducer, micro-nano plugging agent, viscosity reducer and barite, and continue stirring and curing to form a stable colloidal suspension system, thus obtaining the wellbore strengthening oil-based drilling fluid system.

10. The preparation method according to claim 9, characterized in that, The preparation method of the micro / nano plugging agent is as follows: (1) Add nano-silica to water, then add silane coupling agent, and disperse by ultrasonication to obtain mixture A; Mixture A was heated in a water bath while stirring, and then centrifuged to obtain the product. The product was dried to obtain APTES-SiO2; (2) APTES-SiO2 was ultrasonically dispersed in water, and styrene, buffer, sodium dodecyl sulfate and nonylphenol polyoxyethylene ether were added. The mixture was stirred in a water bath and nitrogen was introduced to remove air, thus obtaining a pre-emulsion. (3) Add the initiator to the pre-emulsion and stir in a water bath to obtain mixture B; (4) Centrifuge, wash and dry the mixture B to obtain PS-SiO2, which is a micro-nano sealing agent.

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